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Lower hybrid waves (LHW) are used for non-inductive current drive in many tokamaks. However, additionally to the current drive itself, parasitic particle acceleration in the region just in front of the RF launcher is observed. These particles are dangerous for plasma-facing components, which are magnetically connected with the region of particle acceleration, especially if high LHW power is used (so called �hot spots� have already been observed in tokamaks JET and Tore Supra). Theory suggests a mechanism of the particle acceleration by absorption of higher spatial harmonics in the antenna spectrum and enhancement of this acceleration or even acceleration without presence of the high LHW harmonics by formation of random toroidal electric fields. Experimental assessment of the relative magnitude of these two mechanisms has not been done yet. A small tokamak CASTOR (R/a=0.4/0.85m) with low plasma energy density and short pulses (20ms) offers a unique possibility to carry out probe measurements in front of the grill antenna (three-waveguide multijunction grill, circularly shaped with r=86mm) and in this way to provide direct information about the local electric fields in this region. It has been already shown in that radically very narrow layer (several mm only), with a dip in floating potential V(fl) up to �200V (potential �well�), is formed just in this region if LHW is launched in the CASTOR (power up to 30kW). This dip was interpreted as arising due to the presence of electrons accelerated just in this layer.

Additional information

Authors: ZACEK F, Association Euratom/IPP.CR, Prague (CZ);PETRZILKA V, Association Euratom/IPP.CR, Prague (CZ);DEVYNCK P, Association Euratom-CEA, CEA/DSM/DRFC, CEA-Cadarache, Saint Paul Lez Durance (FR);GONICHE M, Association Euratom-CEA, CEA/DSM/DRFC, CEA-Cadarache, Saint Paul Lez Durance (FR);NANOBASHVILI S, Institute of Physics, Tbilisi (GE)
Bibliographic Reference: An oral paper given at: 30th EPS Conference on Controlled Fusion and Plasma Physics Organised by: European Physical Society Held at: St. Petersburg, Russia, 7-11 July 2003 Proceedings available online at:
Availability: Available from Association EURATOM-CEA, Département de Recherches sur la Fusion Contrôlée, CEA Cadarache, F-13108 St Paul-Lez-Durance, France Tel: (+33) 4 42 25 70 01; Fax: (+33) 4 42 25 64 21 E-mail:
Record Number: 200317061 / Last updated on: 2003-10-29
Original language: en
Available languages: en
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